1. Field of the Invention
The present invention relates to an ink jet printer, and particularly to an ink jet printer for forming an image by irradiating ink with ultraviolet rays to cure the ink.
2. Description of Related Art
An ink jet printer having a plurality of recording heads and a plurality of ultraviolet ray irradiating devices has been recently used. Each recording head is provided with a plurality of nozzles for jetting ink to be cured by irradiating with ultraviolet rays, and each ultraviolet ray irradiating device irradiates the ink with ultraviolet rays to cure the ink (For example, refer to Published Japanese Patent Publication (Tokkaisyo) S60-132767).
As an ultraviolet ray source for irradiating a recording medium with ultraviolet rays, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, a light emitting diode (LED), a laser diode or the like is used in the earlier development. In case of the hot cathode tube, the cold cathode tube, the light emitting diode (LED), the laser diode and the like, the ultraviolet ray has a single wavelength at an emitted light wavelength peak. In an earlier developed ink jet printer, for example, a plurality of rod-shaped cold cathode tubes are arranged in the ultraviolet ray irradiating device to emit ultraviolet rays having a single wavelength at an emitted light wavelength peak.
Further, to form an image on a recording medium which is made of a material not absorbing ink such as a film made of resin, metal or the like, an ink composition (for example, refer to Published Japanese Patent Publication (Tokkaihei) H3-216379) including a component to be polymerized by irradiating with ultraviolet rays and an ink composition (for example, refer to Published Japanese Patent Publication (Tokkaihei) H3-216379) including a color material, an ultraviolet ray curing agent, a photochemical polymerization initiator and the like have been proposed (for example, refer to the specification of U.S. Pat. No. 5,623,001).
For example, the color material dissolving or dispersing in a main component of a polymerizing compound is used for an ultraviolet ray curable ink. In view of the weather-resist property of the color material, pigment is preferable as the color material.
However, in the earlier developed ink jet printer using the high pressure mercury lamps or the metal halide lamps as the ultraviolet ray sources, the size of the high pressure mercury lamp or the metal halide lamp is not so small. Therefore, a problem is arisen that the ink jet printer is manufactured in a large scale. Further, because a carriage holding the ultraviolet ray irradiating devices becomes heavy, another problem is arisen that a moving speed of the carriage is decelerated and an image forming efficiency deteriorates.
On the other hand, in the earlier developed ink jet printer using the hot cathode tubes, the cold cathode tubes, the LEDs, the laser diodes or the like as the ultraviolet ray sources, ultraviolet rays having only a single peak wavelength are emitted. However, because sensitivity of the ultraviolet ray curable ink to the ultraviolet rays of a wavelength depends on the type of the pigment used as the color material of the ink, the wavelength of the ultraviolet rays appropriate to the easily curing of the ultraviolet ray curable ink depends on the type of the pigment. Accordingly, in the earlier developed ink jet printer, when the ink has not sufficiently high sensitivity to the ultraviolet rays having a wavelength at a single light emitting wavelength peak, it is difficult to cure the ink, and a problem is arisen that the image quality of the formed image deteriorates.